The present invention relates to techniques for allocating resources for packet mode data transmission.
It is applied to packet transmission systems wherein transmission resources are shared by multiplexed data flows intended for several users. Each block transmitted on such a resource contains an identity of the flow from which the data which it comprises emanate. The user terminals which share the resource receive at least the part of each block which contains the flow identity, thereby enabling them to determine whether they are concerned by the data of the block.
The invention applies in particular to radio communication systems of GPRS (“General Packet Radio Service”) type. These systems have been developed to allow the packet mode transmission of data in cellular networks of GSM (“Global System for Mobile communications”) type.
GSM networks use a of Time Division Multiple Access (TDMA) scheme in which the physical channels defined in each cell correspond to recurrent time slots on a carrier frequency. These time slots repeat at a frame rate, each frame being composed of eight slots. This multiplexing scheme, intended originally for circuit-mode transmissions, has been adopted to support a packet service, namely GPRS. On the uplink path (from the mobile stations to the network), access to the GPRS physical data channel is controlled by commands supplied by the network. On the downlink path (from the network to the mobile stations), the network selects a user flow for each occurrence of the time slot on the physical channel.
A GPRS data channel is allocated temporarily, when data are to be transmitted. Temporary block flows (TBFs) are thus constantly created and deleted.
In this context, the management of the throughputs supplied to the various flows is a complex problem. It is theoretically possible to search at each instant for the optimum allocation of resources as a function of the throughputs requested for the various active flows and of the number (fixed or variable) of physical channels dedicated to the GPRS service in the cell. However, in practice, this optimization requires a prohibitive quantity of calculations, given the very frequent creation and deletions of TBFs. Moreover, account must be taken of the fact that certain flows have priority over others, as a function of the subscriptions taken out, and the fact that certain terminals may have different reception capacities in terms of number of slots per frame.
An object of the present invention is to propose a throughput management mode which takes these constraints into account and which is relatively simple to implement.